In general, liquid crystal displays have a liquid crystal panel wherein a laminated optical film comprising a polarizer is adhered onto each of two surfaces of a liquid crystal cell, and the liquid crystal cell is made of a liquid crystal material sandwiched between two glass plates. As this polarizer, there is generally used a drawn film obtained by dyeing a polyvinyl alcohol (PVA) based film with iodine or the like, and then drawing the film uniaxially. This polarizer is a polarizer exhibiting absorption dichroism.
As the display performance of liquid crystal displays has been improved in recent years, polarizers which have a higher transmittance and a higher polarization degree have been desired. In order to obtain a polarizer high in transmittance, a film which is made of a polyvinyl alcohol based material having a high polymerization degree is used. Moreover, in order to obtain a polarizer high in polarization degree, a film which is drawn at a higher draw ratio is used (see, for example, Patent Document 1).
However, it is known that a break called crack is easily generated in any films drawn at a high draw ratio. This crack is generated in parallel to the direction in which the film is drawn. It is guessed that this crack is generated since the film-drawn direction and the direction perpendicular thereto are different from each other in thermal shrinkage behavior or the linear expansion coefficient. The crack is more easily generated in a film drawn at a higher draw ratio. When a polarizer wherein a crack is generated is used, the display performance of the liquid crystal display is damaged.
On the other hand, a large-area polarizer that can be used in a large-sized liquid crystal televisional image-receiver has been desired as the size of liquid crystal televisional image-receivers has been becoming large. This is because it is preferred that the polarizer used in a liquid crystal display or the like be seamless. However, about large-area drawn films, the probability of the generation of a crack therein becomes high when the films are produced. Furthermore, in order to produce large-area drawn films, a large-scale drawing facility is required. In order to arrange this drawing facility, a large facility investment is required.
Thus, for example, a technique disclosed in Patent Document 2 is known as a method that neither causes the generation of a crack nor requires any large drawing facility. Specifically, Patent Document 2 proposes a technique of using a polarizing fiber to form a polarizing woven cloth, and coating this polarizing woven cloth with a transparent resin to form a polarizing filter. According to this technique, no drawn film is used; thus, the filter is not cracked in light of the structure thereof, and further no large-scale drawing facility is required.
However, the polarizing filter described in Patent Document 2 is not developed for being used in a liquid crystal display. For this reason, in the polarizing filter, the presence distribution of its polarizing fibers varies, so that the unevenness of transmitted light emerges remarkably. Moreover, in the polarizing filter, light is refracted or reflected on the interfaces between the polarizing fibers and the transparent resin in accordance with the difference between the refractive indexes of the polarizing fibers and that of the coating transparent resin. For this polarizing filter, the transmittance and the polarization degree thereof are not sufficient for liquid crystal displays. Accordingly, the polarizing filter described in Patent Document 2 cannot be used as it is for a liquid crystal display.
Further, as the method for dyeing a polarizing fiber, a method of kneading a resin and a dye, and then spinning the kneaded product, or a method of forming pellets (chips) dyed with a dye in advance and then blending the pellets when a fiber spinning is made is known (see, for example, Patent Documents 3 and 4). However, in any one of the methods, it is necessary for adjusting the color tone of a polarizer to incorporate plural dyes to a polarizing fiber therefor during producing the fiber. Therefore, according to the methods, after the production of a polarizing fiber, the color tone thereof cannot be adjusted.
Thus, proposed is a technique of using a polarizing fiber and a birefringent fiber together, thereby overcoming the unevenness of the transmittance, preventing the refraction or reflection of light on the interface between the polarizing fiber and a transparent resin, and making it possible to adjust the color tone of the polarizing fiber after the fiber is made into a fiber spinning (see, for example, Patent Document 5).    Patent Document 1: JP-A-8-190015    Patent Document 2: JP-A-6-130223    Patent Document 3: JP-A-10-130946    Patent Document 4: JP-A-10-170720    Patent Document 5: JP-A-2006-126313